DOCSLIB.ORG

Theta Liftings on Higher Covers of Symplectic Groups

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Theta Liftings on Higher Covers of Symplectic Groups Theta liftings on higher covers of symplectic groups Author: Spencer Leslie Persistent link: http://hdl.handle.net/2345/bc-ir:107937 This work is posted on eScholarship@BC, Boston College University Libraries. Boston College Electronic Thesis or Dissertation, 2018 Copyright is held by the author, with all rights reserved, unless otherwise noted. Theta liftings on higher covers of symplectic groups Spencer Leslie A dissertation submitted to the Faculty of the Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy Boston College Morrissey College of Arts and Sciences Graduate School May 2018 c Copyright 2018 Spencer Leslie Theta liftings on higher covers of symplectic groups Spencer Leslie Thesis advisor: Solomon Friedberg We study a new lifting of automorphic representations using the theta representa- tion Θ on the 4-fold cover of the symplectic group, Sp2r(A). This lifting produces the first examples of CAP representations on higher degree metaplectic covering groups. Central to our analysis is the identification of the maximal nilpotent orbit associated to Θ. We conjecture a natural extension of Arthur's parameterization of the discrete spectrum to Sp2r(A). Assuming this, we compute the effect of our lift on Arthur parameters and show that the parameter of a representation in the image of the lift is non-tempered. We conclude by relating the lifting to the dimension equation of Ginzburg to predict the first non-trivial lift of a generic cuspidal representation of Sp2r(A). Contents 1 Introduction1 1.1 Theta functions and liftings.......................1 1.2 Main Results...............................6 2 Notations and Preliminaries 13 2.1 Subgroups and characters........................ 13 2.2 Formalism on roots............................ 16 3 Theta Representations: Local and Global Theory 17 3.1 Theta Representations: local theory................... 18 3.2 Theta Representations: global theory.................. 27 4 Fourier Coefficients Associated to a Nilpotent Orbit 31 4.1 Algebraic Setup.............................. 32 4.2 Local Fourier-Jacobi Coefficients..................... 37 4.3 Root Exchange.............................. 41 5 Fourier-Whittaker Coefficients: Identification of the Orbit 47 5.1 Vanishing Statements........................... 48 5.2 Non-Vanishing Statement........................ 56 6 Unramified Local Lifting and Satake Parameters 66 6.1 Statement of the local correspondence.................. 66 7 The Global Lifting and Cuspidality 77 7.1 Global Lifting............................... 77 7.2 Towering property of the theta lift.................... 79 8 CAP Representations and Arthur Parameters 89 8.1 CAP representations........................... 89 8.2 Conjectural Shimura Lift......................... 92 8.3 Arthur's conjectures........................... 94 9 Generic Lifts and the Dimension Equation 97 iv Contents v 10 Future Directions 103 A Appendices to Part 1 107 A.1 Local filtration.............................. 107 A.2 Technical Lemmas............................ 108 Bibliography 112 Citations to Previous Work This thesis is based on [Les17]. vi Acknowledgments To begin, I want to thank my advisor Sol Friedberg for several things: for first informing me about the program at BC and encouraging me to apply; for careful guid- ance into the world of automorphic forms; and for his unconditional mathematical, professional, and personal support over the past five years. I wish also to thank David Treumann for supporting me as though I was his own student and for generally being a joy to talk math with. Additionally, I thank Mark Reeder, not only for his teaching fantastic courses, but for his very useful advise at multiple points of my time as a graduate student. Finally, I thank Ben Howard for his active role in the \number theory" side of the department running several formative seminars. I would like to give special thanks to David Ginzburg for asking the question which ultimately led to this thesis, as well as for being generous with his ideas. Beyond this, there are several people I wish to thank for useful mathematical discussions, many of which were on other projects but all proved enjoyable and helpful: Arkady Berenstein, Yuanqing Cai, Wee Teck Gan, Jayce Getz, Kyle Hayden, Gus Lonergan, Ari Shnidman, Marty Weissman, Shucheng Yu, Lei Zhang, and Melissa Zhang. I thank you all. On a personal note, I want to give a special shoutout to Kyle Hayden for being a good friend throughout graduate school. Also, I would never have made it to graduate school were it not for the tireless work of James Cook, and I thank him for this. Finally and most importantly, I want to thank Casey Leslie, without whom this thesis would not have been possible and with whom the past five years have been a joy. vii To my best friend Casey. viii Chapter 1 Introduction 1.1 Theta functions and liftings One of the first modular functions ever studied was the classical theta function of Jacobi, which may be written as X πin2τ Θ(τ) = e ; where τ 2 C; Im(τ) > 0: n2Z While variations of this function were studied as far back as Euler, one of the most important early applications of the theta function comes in Riemann's second proof of the functional equation of the eponymous zeta function. The key property of this function is the functional equation 1 −1 Θ(τ) = p Θ ; τ τ which implies, along with the obvious invariance Θ(τ + 2) = Θ(τ), that Θ is a 1 modular form of weight 2 . Today, we understand, thanks to Weil [Wei64], that the theory of half-integral weight modular forms may be understood as studying certain automorphic representations of the metaplectic double cover Mp2(R) of the 1 2 Chapter 1: Introduction group SL2(R). Moreover, the Jacobi theta function corresponds to a particularly important automorphic representation ! known as the Segal-Shale-Weil(-oscillator) representation. In particular, the theory of automorphic forms on the non-linear covers of reductive groups is as old as the theory of modular forms itself. Let K be a number field, and let G be a reductive group over K. Motivated by the classical theory of theta functions and other applications to number theory ([KP84], [Kub69]), the theory of automorphic forms on covers of the group G(A), where A is the ring of adeles of K, has enjoyed much recent attention (for example, [KP84, Wei03, Wei14, GG14, FG17, BBF11, Gao18b]). While many people have developed the theory of topological covering groups of G(A), we will use the theory of Brylinski and Deligne [BD01] to describe the groups in which we are interested. Assuming K contain the nth roots of unity, Brylinski and Deligne classify degree n topological extensions GA of G(A) by µn(K) which arise from the algebraic K-theory of the field K. More precisely, viewing G as a sheaf of groups on the big Zariski site over Spec(K), Brylinski-Deligne characterize the objects in the Picard category CExt(G; K2) of central extensions (of sheaves) of G by Quillen's algebraic K-theory sheaf K2: That is, an object G 2 CExt(G; K2) is a sheaf of groups such that there is a short exact sequence 1 −! K2 −! G −! G −! 1 (1.1) with the image of K2 central in G. The classification is particularly simple when G is split, and for G semi-simple and simply connected, CExt(G; K2) is discrete with a single generator, essentially recovering Steinberg's universal extension. This classifi- cation of (BD-)covering groups works over a general base scheme S; in particular, we have an analogous theory over local fields F . Chapter 1: Introduction 3 Given a BD-extension G, we obtain a degree n topological covering group π 1 −! µn(K) −! G(A) −! G(A) −! 1 th (·;·)n by taking A-points of (1.1) and pushing out by the n -Hilbert symbol K2(A) −−−! th µn(A) = µn(K): The reason for studying central extensions by n -roots of unity is that, as noticed by Weil [Wei64], the nth-order reciprocity theorem of class field theory implies that the cover π splits over the discrete subgroup G(K) ⊂ G(A). Thus, upon fixing a section over the rational points, we may meaningfully study automorphic forms on G(A). This construction recovers essentially all topological covering groups that have arisen in automorphic representation theory. One reason for working with this formalism is that there is a reasonable notion of an L-group for such covering groups. Given an n-fold topological BD-covering _ group G, we may associate to it a natural complex dual group G , which can be distinct from the dual group of G. Recently, Weissman has put forward a promising candidate, LG; for the L-group of such covering groups (see [Wei14] and [Wei15]) as an extension _ L 1 −! G −! G −! WK −! 1: (1.2) It is thus important to test if this L-group allows us to extend Langlands functori- ality and Arthur's conjectures to the case of BD-covering groups. For example, the construction of the metaplectic tensor product has been shown to be functorial by Gan [Gan16]. Historically, the metaplectic 2-fold cover of the symplectic group, Mp(W ), where (W; h·; ·i) is a symplectic vector space over K, is the first example of a BD-covering group to be studied. Much is known about the representation theory of Mp(W ); in 4 Chapter 1: Introduction particular, the local Langlands correspondence1 has been extended to this group via work of Adams-Barbasch [AB95], [AB98] in the real case, and Gan-Savin [GS12] in the nonarchimedean case. A primary tool in the study of the representation theory of Mp(W ) has been the theta correspondence, which is an integral lifting construction 2 utilizing the oscillator representation ! , the generalization of the classical theta representation mentioned above. We pause here to sketch what we mean by an \integral lifting construction".
Load more

Recommended publications
  • Rank One Reducibility for Metapletic Groups Via Theta Correspondence
    Rank one reducibility for metapletic groups via theta correspondence Marcela Hanzer, Goran Mui´c Abstract We calculate reducibility for the representations of metaplectic groups induced from cuspidal representations of maximal parabolic subgroups via theta correspondence, in terms of the analogous repre- sentations of the odd orthogonal groups. We also describe the lifts of all relevant subquotients. 1 Introduction In this paper we study rank-one reducibility for the non{trivial double Sp^(n) cover of symplectic group Sp(n) over a non{Archimedean local field of charac- teristic different than two using theta correspondence. This paper combined with [8] is a fundamental step in a systematic study of smooth complex rep- resentations of metaplectic groups. We expect application in the theory of automorphic forms where metaplectic groups play a prominent role. We recall that the group Sp^(n) is not a linear algebraic group. Thus, it is not in the framework of the usual theory for p-adic groups. Neverthe- less, some basic algebraic facts [8] are true here. More precisely, based on a fundamental work of Bernstein and Zelevinsky ([2], [3], [26]) we checked that the basic notions of the representation theory of p{adic groups hold for metaplectic groups (some of that is already well{known from the previous works of Kudla [10], [9] and the book [15]). As usual, a parabolic subgroup of Sp^(n) is the preimage Pe of a parabolic subgroup P of Sp(n). If we write P = MN for a Levi decomposition, then the unipotent radical N lifts to Sp^(n): So, we have a decomposition Pe = MNf .
    [Show full text]
  • R–Groups for Metaplectic Groups∗
    R{groups for metaplectic groups∗ Marcela Hanzery1 1Department of Mathematics, University of Zagreb, Croatia Abstract In this short note, we completely describe a parabolically induced representation Sp^(2n;F ) IndP (σ); in particular, its length and multiplicities. Here, Sp^(2n; F ) is a p{adic metaplectic group, and σ is a discrete series representation of a Levi subgroup of P: A multiplicity one result follows. 1 Introduction A knowledge of R{groups (in all their variants{classical, Arthur, etc.) is very important in understanding the representation theory of reductive p{adic groups, especially their unitary duals. Let G be a reductive p{adic group with a parabolic subgroup P = MN where M is a Levi subgroup. Assume σ is a discrete series (complex) representation of M: Then, it is G important to understand how the representation IndP (σ) reduces: whether it is reducible, and if it is reducible, whether all the irreducible subquotients appear with multiplicity one. These questions are answered by knowing the structure of the commuting algebra C(σ); G i.e., the intertwining algebra of IndP (σ): It is already known from the work of Casselman that the dimension of C(σ) is bounded by the cardinality of W (σ); the subgroup of the Weyl group of G fixing the representation σ: The precise structure of C(σ) is given by a certain subgroup of W (σ); called the R{group of σ: This approach to understanding the G structure of IndP (σ) goes back to the work of Knapp and Stein on real groups and principal series representations.
    [Show full text]
  • On First Occurrence in the Local Theta Correspondence
    On First Occurrence in the Local Theta Correspondence Stephen S. Kudla∗ and Stephen Rallis† Abstract. This paper discusses a conservation conjecture for the first oc- currence indices. Such indices record the first occurrence of an irreducible admissible representation π of a fixed group G in the local theta correspon- dence as the second member of a dual pair (G, G) runs over the isometry groups in a Witt tower. For example, for a fixed nonarchimedean local field F and for a fixed quadratic character χ of F ×, there are two Witt towers + − ± {Vm } and {Vm }, where the quadratic space Vm has dimension m,character ± ± χ and Hasse invariant ±1. If mχ (π)isthe dimension of the space Vm for which the irreducible admissible representation π of Spn(F ) first occurs in the ± theta correspondence for the dual pair (Spn(F ),O(Vm )), then we conjecture that + − mχ (π)+mχ (π)=4n +4. We prove this conjecture in many cases, in particular, when π is a supercus- pidal representation. 2000 Mathematics Subject Classification: primary 11F27; secondary 22E50. 0. Introduction A basic step in understanding the local theta correspondence is the descrip- tion of the behavior of the correspondence as one group in the reductive dual pair varies in a Witt tower, [18]. The combination of this Witt tower tech- nique, with the method of ‘doubling’, [4], [18], and the local ‘doubling’ zeta integrals, [16], [17], lies behind much of our qualitative understanding of the correspondence. In this paper1,inthe case of a nonarchimedean local field, ∗Partially supported by NSF Grant DMS-0200292 and by a Max-Planck Research Prize from the Max-Planck Society and Alexander von Humboldt Stiftung.
    [Show full text]
  • Singular Theta Lifts and Near-Central Special Values of Rankin-Selberg L-Functions
    Singular theta lifts and near-central special values of Rankin-Selberg L-functions Luis E. Garcia Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences COLUMBIA UNIVERSITY 2013 c 2013 Luis E. Garcia All Rights Reserved ABSTRACT Singular theta lifts and near-central special values of Rankin-Selberg L-functions Luis E. Garcia In this thesis we study integrals of a product of two automorphic forms of weight 2 on a Shimura curve over Q against a function on the curve with logarithmic singularities at CM points obtained as a Borcherds lift. We prove a formula relating periods of this type to a near-central special value of a Rankin-Selberg L-function. The results provide evidence for Beilinson's conjectures on special values of L-functions. Table of Contents 1 Introduction 1 1.1 Statement of the main theorem . 1 1.2 Outline of the thesis . 3 1.3 Beilinson's conjectures . 5 1.4 The case of Rankin-Selberg L-functions . 10 1.5 An example . 12 1.6 Notations and measures . 14 2 Theta Correspondence for (Sp4;O4) 18 2.1 Four-dimensional quadratic spaces and their orthogonal groups . 18 2.2 Yoshida lifts . 20 2.3 Weil representation . 21 2.4 Non-archimedean correspondence . 21 2.5 Archimedean correspondence . 24 2.6 Special Schwartz forms . 27 2.7 Siegel-Weil formula . 30 3 Singular theta lifts 32 3.1 Borcherds lifts . 32 3.2 Harmonic Whittaker forms . 38 4 Local Zeta integrals 42 4.1 Doubling Integrals .
    [Show full text]
  • The Theta Correspondence Over R
    The Theta Correspondence over R Jeffrey Adams May 3, 2007 1 Introduction These notes were written for the workshop on the Theta correspondence held at the University of Maryland, May 1994. They have circulated informally for many years. Except for minor changes and some improvements to the references they have not been changed. There have been too many develop- ments in the field since 1994 to try to bring them up to date. This is dedicated to Roger Howe, who introduced me to representation theory in graduate school in 1977. 2 Fock model: complex Lie algebra The Fock model is the algebraic oscillator representation: it is the (g; K) module of the oscillator representation of Sp(2n; R). The basic references e are [6],[7], and [47]. See also [11],[17] and [18]. The presentation here is due f to Steve Kudla (unpublished); a similar treatment is found in [49], as well as [51]. In this section we define the oscillator representation of the complex Heisenberg and symplectic Lie algebras. Let be a non{trivial linear form on C, i.e. fix λ 2 C× and let (z) = λz (z 2 C). Definition 2.1 Let W be a vector space with a symplectic form h; i, possibly degenerate. Let Ω(W ) = T (W )=I 1 where T is the tensor algebra of W and I is the two{sided ideal generated by elements of the form v ⊗ w − w ⊗ v − hv; wi (v; w 2 W ): This is an associative algebra, sometimes referred to as the quantum algebra. For example if hv; wi = 0 for all v; w, then Ω(W ) is isomorphic to the polynomial algebra on W .
    [Show full text]
  • Introduction to the Theta Correspondence
    Do you even lift? Introduction to the theta correspondence Kevin Chang June 15, 2021 Contents 1 Introduction 1 1.1 Notation and conventions . .2 2 The Weil representation and the theta correspondence 3 2.1 The Weil representation over a p-adic field . .3 2.2 The Weil representation over a finite field . .5 2.3 Main example: The theta correspondence for (Sp(2); O+(4)) ...6 3 The preservation principle 7 3.1 The preservation principle for the local theta correspondence . .7 3.2 Main example: A chain of supercuspidals . .8 3.3 The preservation principle over a finite field . .9 3.4 Main example: The preservation principle for (Sp(2); O+(4)) ..9 4 Compatibility 10 4.1 A result of Pan . 10 + 4.2 Main example: Compatibility between p-adic (Sp(V2); O(V6 )) and finite (SL(2); O−(2) × O+(4)) .................. 11 4.2.1 Components are not cuspidal . 11 4.2.2 Components are cuspidal . 13 5 Continuation of the main example 13 1 Introduction As every Hollywood executive knows, if there’s ever a good thing, it needs to be milked dry. The local theta correspondence is a powerful method for pro- ducing representations of p-adic groups following precisely this philosophy. In slightly less vague terms, the local theta correspondence is a matching between certain representations of certain pairs of p-adic reductive groups known as dual reductive pairs. If we have a chain of p-adic groups with each consecutive pair a 1 dual reductive pair and a representation of the first group in the chain, we can try to produce a chain of representations by repeatedly applying the local theta correspondence.
    [Show full text]
  • Notes on the Local Theta Correspondence
    NOTES ON THE LOCAL THETA CORRESPONDENCE Stephen S. Kudla Department of Mathematics University of Maryland College Park, MD 20742, U.S.A. email: [email protected] c 1996 Stephen S. Kudla Introduction These notes are intended to provide an introduction to the theory of the theta cor- respondence over a nonarchimdean local field. They form the basis and background for a series of ten lectures to be given as part of the European School in Group Theory at Schloß Hirschberg in September, 1996. Here is a rough outline of what they contain: Chapter I. The Heisenberg group, the metaplectic group, the Weil representation, the Rao cocycle, and Schr¨odinger models. Chapter II. Reductive dual pairs, the theta correspondence, the Howe duality principle, restriction of the metaplectic cover, the Weil representation for the dual pair (O(V ),Sp(W )) , scaling. Chapter III. Witt towers, parabolic subgroups, the Bernstein-Zelevinsky classifi- cation, persistence and stable range, first occurrence indices, the trivial represen- tation, supercuspidals, compatibility with the Bernstein-Zelevinsky classification, Jacquet functors of the Weil representation. Chapter IV. Seesaw dual pairs, degenerate principal series and their restrictions, proofs of some results of Chapter III. Typeset by AMS-TEX 1 2 STEPHEN S. KUDLA Chapter V. First occurrence indices for pairs of Witt towers, conservation and dichotomy conjectures, quotients of degenerate principal series, zeta integrals. Chapter VI. Low dimensional examples, chains of supercuspidals, behavior of unramified representations in the correspondence, L-homomorphisms and functori- ality These notes overlap with the book of Moeglin, Vigneras and Waldspurger, [46], at a number of places, but the overall point of view is somewhat different.
    [Show full text]
  • Theta Correspondence and Representation Theory
    THETA CORRESPONDENCE AND REPRESENTATION THEORY 京都大学 総合人間学部 西山 享 (KYO NISHIYAMA) FACULTY OF IHS, KYOTO UNIVERSITY SAKYO, KYOTO 606-8501, JAPAN Abstract. After reviewing the relation between the theta integral (= theta lifting) and Howe correspondence, we give an example of the preservation of the associated cycles by the theta lifting (joint work with C.-B. Zhu). Namely, let (G, G0) be a type I dual pair strictly in the stable range (we assume that G0 is the smaller member), and π0 a unitary highest weight module of Gf0. Then the associated cycle of the theta lift π = θ(π0) of π0 can be given as AC(θ(π0)) = θ(AC(π0)), where the theta lifting of associated cycle is naturally defined using the lifting of nilpotent orbits. We also give a naive introduction to the basic property of associated cycles and the lifting of nilpotent orbits. 1. Theta integral The content of this section is mainly quoted from [10, 11] and [4]. Let F be a number field and A a ring of adeles of F . For simplicity, we consider one of type I dual pairs defined over F in the following. It is constructed as follows. Take a vector space V /F with non-degenerate symmetric bilinear form (, ) = (, )V 0 0 V /F with non-degenerate skew-symmetric bilinear form (, ) = (, )V 0 0 Then W = V ⊗F V inherits a skew-symmetric form defined by (, )W = (, )V ⊗F (, )V 0 . We put ( G = O(V ) orthogonal group G0 = Sp(V 0) symplectic group They are naturally subgroups of Sp(W ) commuting with each other, which form a type 0 0 I dual pair (G, G ) in Sp(W ).
    [Show full text]
  • PARITY PRESERVATION of K-TYPES UNDER THETA CORRESPONDENCE 2 Is the Multiplicity of Σ in V
    PARITY PRESERVATION OF K-TYPES UNDER THETA CORRESPONDENCE XIANG FAN Abstract. This note shows a property of degree-parity preservation for K-types un- der Howe’s theta correspondence. As its application, we deduce the preservation of parity of all K-types occurring in an arbitrary irreducible (g, K)-module of any Lie group in reductive dual pairs. 1. Degree-parity Preservation Howe’s duality correspondence of irreducible admissible representations for reductive dual pairs was introduced by Roger Howe in the 1970s. It is also called the theta correspondence as an extension of Weil’s representation-theoretic approach to classical θ-series. In this short note, a degree-parity preservation property (Theorem 1.5) for K-types is shown for the local theta correspondence of reductive Lie groups, with an interesting application, Theorem 2.1 (or Theorem 2.6 in its general form), which asserts the preservation of parity of all K-types occurring in an arbitrary irreducible admissible representation of a Lie group in reductive dual pairs. For a continuous admissible representation of a real reductive Lie group G, as we focus on its K-spectrum, we may replace it by its Harish-Chandra (g, K)-module (consisting of its K-finite smooth vectors). Here K is a maximal compact subgroup of G, and g is the complexified Lie algebra of G. Throughout this note, we use upper case Latin letters (e.g., G, G′, K, T ) to denote Lie groups, and the corresponding lower case Gothic letters (e.g., g, g′, k, t) to indicate their complexified Lie algebras.
    [Show full text]
  • Coincidence of Algebraic and Smooth Theta Correspondences
    REPRESENTATION THEORY An Electronic Journal of the American Mathematical Society Volume 21, Pages 458–466 (November 1, 2017) http://dx.doi.org/10.1090/ert/508 COINCIDENCE OF ALGEBRAIC AND SMOOTH THETA CORRESPONDENCES YIXIN BAO AND BINYONG SUN Abstract. An “automatic continuity” question has naturally occurred since Roger Howe established the local theta correspondence over R:Doestheal- gebraic version of local theta correspondence over R agree with the smooth version? We show that the answer is yes, at least when the concerning dual pair has no quaternionic type I irreducible factor. 1. Introduction In his seminal work [Ho3], Roger Howe established the smooth version of lo- cal theta correspondence over R as a consequence of its algebraic analogue (see [Ho3, Theorem 1 and Theorem 2.1]). Since then, it has been expected that the smooth version coincides with the algebraic version. Our main goal is to prove this coincidence, at least when the dual pair concerned has no quaternionic type I irreducible factor. In this latter case, we obtain a partial result (cf. Proposition 3.2). The proof is a rather direct application of the conservation relations which are established in [SZ]. To be precise, let W be a finite-dimensional symplectic space over R with sym- plectic form , W .Denotebyτ the involution of EndR(W ) specified by τ (1.1) x · u, vW = u, x · vW ,u,v∈ W, x ∈ EndR(W ). Let (A, A )beapairofτ-stable semisimple real subalgebras of EndR(W )whichare mutual centralizers of each other in EndR(W ). Put G := A Sp(W )andG := A Sp(W ), which are closed subgroups of the symplectic group Sp(W ).
    [Show full text]
  • GEOMETRIC REDUCTIVE DUAL PAIRS and a MOD P THETA CORRESPONDENCE
    GEOMETRIC REDUCTIVE DUAL PAIRS AND A MOD p THETA CORRESPONDENCE SUG WOO SHIN Abstract. This paper aims to recast the theory of theta correspondence in the geometric context of abelian schemes and nondegenerate line bundles, which replace the role of symplectic vector spaces, continuing our previous work. We start by formulating the notion of reductive dual pairs which fit well with our notion of Weil representations and metaplectic group functors constructed in the earlier work. When specialized to the case of base scheme Spec Fp, our work provides an experimental framework for a mod p theta correspondence for p-adic reductive groups. In the case of type II pairs, two results are obtained on the structure of mod p Weil representations. First, the Weil representation turns out to have few quotients, which tells us that the naive analogue of the classical theta correspondence is hopeless and would demand a new approach. Second, a weak analogue of the unramified version of Howe's conjecture still holds. 1. Introduction 1.1. Basic ingredients. 1 In x1.1 of [Shi], we mentioned that the following are needed to formulate the classical theta correspondence. That paper studied (i), (ii) and (iii) in the context of abelian schemes and nondegenerate line bundles. Once (iii) is obtained from (i) and (ii) and realized on explicit models, it is often harmless to forget (i) and (ii). (i) a p-adic Heisenberg group arising from a symplectic vector space (V; h·; ·i) over Qp, (ii) Stone Von Neumann theorem and Schur's lemma for representations of the Heisenberg group, (iii) the Weil representations of the p-adic metaplectic group Mp(V; h·; ·i), and (iv) reductive dual pairs in Sp(V; h·; ·i).
    [Show full text]
  • Arxiv:1802.01774V2 [Math.RT] 14 Aug 2018 Tdvreis Soitdcce,Ascae Characters
    LOCAL THETA CORRESPONDENCE AND NILPOTENT INVARIANTS CHEN-BO ZHU Dedicated to Joseph Bernstein on the occasion of his seventy-second birthday Abstract. We consider two types of nilpotent invariants associated to smooth representations, namely generalized Whittaker models, and associated charac- ters (in the case of a real reductive group). We survey some recent results on the behavior of these nilpotent invariants under local theta correspondence, and highlight the special role of a certain double fiberation of moment maps. 1. Introduction One of the most fruitful approaches in representation theory is to understand representations through their invariants. Among the most well-known invariants are matrix coefficients (and their growth), and the character of a representation, which are of analytic nature. In the case of a real reductive group, fundamental invariants of algebraic nature include the infinitesimal character and the restriction of the representation to a maximal compact subgroup. Each of the afore-mentioned invariants has played a prominent role in the most important tasks of representa- tion theory, for example in the classification of representations [28, 53]. In the current article, we will be concerned with smooth representations of a reductive group defined over a local field F of characteristic 0. By a smooth representation we mean a smooth representation in the usual sense for F non- Archimedean, namely it is locally constant, and a Casselman-Wallach representa- tion for F Archimedean [4, 59]. The invariants we will consider will be informally referred to as nilpotent invari- ants as they depend on various types of nilpotent orbits and thus reflect various kinds of singularities.
    [Show full text]